A species of Gram-negative aerobic bacteria that is found in the intestine (see coliform bacteria) and is also widely used in microbiological and genetics research. The motile rod-shaped cells ferment lactose and are usually harmless commensals, although certain strains are pathogenic and can cause a severe form of food poisoning. Studies of E. coli laboratory cultures have revealed much about the biology and genetics of prokaryotes and the bacteriophages that infect them; the species is also frequently used in genetic engineering, particularly as a host for gene cloning and the expression of recombinant foreign genes in culture.